Hybrid vehicle

ABSTRACT

A hybrid vehicle includes an engine ( 10 ), a first motor generator (MG 1 ), a second motor generator (MG 2 ), a transmission unit (power transmission unit) ( 40 ), a differential unit ( 50 ), a clutch (CS) and a mechanical oil pump ( 501 ). The hybrid vehicle is able to switch between series-parallel mode in which power of the engine is transmitted via the transmission unit and the differential unit and series mode in which power of the engine is transmitted via the clutch. The differential unit ( 50 ) is a planetary gear mechanism including a sun gear (S 2 ) connected to the first motor generator (MG 1 ), a ring gear (R 2 ) connected to the second motor generator (MG 2 ), and a carrier (CA 2 ) connected to a ring gear (R 1 ) that is an output element of the transmission unit ( 40 ). The mechanical oil pump ( 501 ) is driven by power that is transmitted from the carrier (CA 2 ) of the differential unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a hybrid vehicle.

2. Description of Related Art

There is known a hybrid vehicle including not only an engine, two rotaryelectric machines (first rotary electric machine and second rotaryelectric machine) and a differential unit (power split mechanism) butalso a transmission unit (power transmission unit) between the engineand the differential unit.

A vehicle described in International Application Publication No.2013/114594 is able to switch between motor drive mode (hereinafter,referred to as EV mode) and hybrid mode (hereinafter, referred to as HVmode). In motor drive mode, the engine is stopped, and the power of thesecond rotary electric machine is used. In hybrid mode, the power ofboth the engine and the second rotary electric machine is used. Aseries-parallel mode drive system is employed as an HV drive system. Inseries-parallel mode, the power of the engine is transmitted to thefirst rotary electric machine and is used to generate electric power,while part of the power of the engine is also transmitted to drivewheels via the differential unit.

There is also known a series mode drive system as an HV drive system. Inthe series mode drive system, electric power is generated by using thepower of an engine, and a motor is driven by using the generatedelectric power. In this series mode, the power of the engine is nottransmitted to drive wheels.

The vehicle described in International Application Publication No.2013/114594 is not configured to be able to travel in series modebecause the power of the engine is also transmitted to the drive wheelsvia the differential unit at the time when the power of the engine istransmitted to the first rotary electric machine.

It is conceivable to provide a second path that directly transmits thepower of the engine to the first rotary electric machine in addition toa first path that transmits the power of the engine to the first rotaryelectric machine via the transmission unit (power transmission unit) andthe differential unit and then a clutch is provided in the second path.With this configuration, it is possible to select one of theseries-parallel mode and the series mode. Specifically, it is possibleto select the series-parallel mode by transmitting the power of theengine through the first path (that is, placing the transmission unitprovided in the first path in a power transmitting state and releasingthe clutch provided in the second path). On the other hand, it ispossible to select the series mode by transmitting the power of theengine through the second path (that is, placing the transmission unitprovided in the first path in a neutral state and engaging the clutchprovided in the second path).

In the above configuration, a mechanical oil pump is connected to anylocation in a power transmission path from the engine to the drivewheels, and hydraulic pressure for activating the transmission unitprovided in the first path and the clutch provided in the second path isallowed to be generated by the mechanical oil pump.

However, for example, in the case where the mechanical oil pump isconnected to an input shaft of the transmission unit (power transmissionunit), when the engine is stopped, rotation of the input shaft of thetransmission unit connected to an output shaft of the engine is alsostopped, so it is not possible to activate the mechanical oil pump.

SUMMARY OF THE INVENTION

The invention is directed to, in a hybrid vehicle that is able to selectone of series-parallel mode and series mode, a mechanical oil pump isallowed to be activated in a state where an engine is stopped.

An aspect of the invention provides a hybrid vehicle. The hybrid vehicleincludes an internal combustion engine, a first rotary electric machine,a second rotary electric machine, a power transmission unit, a clutchand a mechanical oil pump. The second rotary electric machine isconfigured to output power to a drive wheel. The power transmission unitincludes an input element, an output element and an engaging portion.The input element is configured to receive power from the internalcombustion engine. The output element is configured to output powerinput to the input element. The engaging portion is configured, toswitch between a non-neutral state where power is transmitted betweenthe input element and the output element and a neutral state where poweris not transmitted between the input element and the output element. Thedifferential unit includes a first rotating element, a second rotatingelement and a third rotating element. The first rotating element isconnected to the first rotary electric machine. The second rotatingelement is connected to the second rotary electric machine and the drivewheel. The third rotating element is connected to the output element.The differential unit is configured such that, when rotation speeds ofany two of the first rotating element, the second rotating element andthe third rotating element are determined, a rotation speed of theremaining one of the first rotating element, the second rotating elementand the third rotating element is determined. The clutch is configuredto switch between an engaged state where power is transmitted from theinternal combustion engine to the first rotary electric machine and areleased state where transmission of power from the internal combustionengine to the first rotary electric machine is interrupted. Power fromthe internal combustion engine is transmitted to the first rotaryelectric machine though at least one of a first path or a second path.The first path is a path through which power is transmitted from theinternal combustion engine to the first rotary electric machine via thepower transmission unit and the differential unit. The second path is apath through which power is transmitted from the internal combustionengine to the first rotary electric machine via a path different fromthe first path. The clutch is provided in the second path. Themechanical oil pump is configured to generate hydraulic pressure foractivating the power transmission unit and the clutch. The mechanicaloil pump is configured to be driven by power that is transmitted fromany one of the first rotating element, second rotating element and thirdrotating element of the differential unit.

With the thus configured hybrid vehicle, it is possible to select one ofthe series-parallel mode and the series mode by controlling the powertransmission unit provided in the first path and the clutch provided inthe second path. In addition, the mechanical oil pump is driven by powerthat is transmitted from not the input element of the power transmissionunit but any one of the first rotating element, second rotating elementand third rotating element of the differential unit. The first rotatingelement, second rotating element and third rotating element of thedifferential unit are rotatable even in a state where rotation of theinput element of the power transmission unit is stopped as a result of astop of the internal combustion engine. Therefore, in the hybrid vehiclethat is able to select one of the series-parallel mode and the seriesmode, it is possible to operate the mechanical oil pump in a state wherethe engine is stopped.

In the hybrid vehicle, the differential unit may be a planetary gearincluding a sun gear, a ring gear, pinions that are in mesh with the sungear and the ring gear, and a carrier that supports the pinions suchthat the pinions are rotatable. The first rotating element, the secondrotating element and the third rotating element may be respectively thesun gear, ring gear and carrier of the planetary gear. The mechanicaloil pump may be connected to the carrier. The mechanical oil pump may beconfigured to be driven by power that is transmitted from the carrier.

With the thus configured hybrid vehicle, because the mechanical oil pumpis connected to the carrier of the differential unit, it is possible tosimplify the configuration around the mechanical oil pump. That is, forexample, when the mechanical oil pump is connected to the ring gearconnected to the drive wheel, a reverse rotation prevention device(one-way clutch, or the like) for preventing reverse rotation of themechanical oil pump is required in the case where the ring gear rotatesin the reverse direction at the time when the vehicle moves backward.However, when the mechanical oil pump is connected to the ring gear ofthe differential unit, such a reverse rotation prevention device is notrequired, so it is possible to simplify the configuration around themechanical oil pump.

The hybrid vehicle may further include an electric oil pump and acontroller. The electric oil pump may be configured to generatehydraulic pressure for activating the power transmission unit and theclutch. The controller may be configured to control the electric oilpump. The controller may be configured to, at the time of switching fromseries-parallel mode to series mode, change a rotation speed of theelectric oil pump based on whether a rotation speed of the internalcombustion engine is lower than a rotation speed of the first rotaryelectric machine. The series-parallel, mode may be a mode in which thehybrid vehicle travels in a state where the power transmission unit isplaced in the non-neutral state and the clutch is placed in the releasedstate. The series mode may be a mode in which the hybrid vehicle travelsin a state where the power transmission unit is placed in the neutralstate and the clutch is placed in the engaged state.

With the thus configured hybrid vehicle, at the time of switching fromthe series-parallel mode to the series mode, when the rotation speed ofthe internal combustion engine is lower than or higher than the rotationspeed of the first rotary electric machine, a temporal change inrotation of the mechanical oil pump occurs. An increase or reduction inhydraulic pressure resulting from a temporal change in rotation of themechanical oil pump is compensated by hydraulic pressure of the electricoil pump. Therefore, it is possible to supply necessary and sufficienthydraulic pressure even in a period of transition of switching from theseries-parallel mode to the series mode.

In the hybrid vehicle, the controller may be configured to, at the timeof switching from the series-parallel mode to the series mode, increasethe rotation speed of the electric oil pump when the rotation speed ofthe internal combustion engine is lower than the rotation speed of thefirst rotary electric machine, and decrease the rotation speed of theelectric oil pump when the rotation speed of the internal combustionengine is higher than the rotation speed of the first rotary electricmachine.

With the thus configured hybrid vehicle, when the rotation speed of theinternal combustion engine is lower than the rotation speed of the firstrotary electric machine, the rotation speed of the mechanical oil pumptemporarily decreases as a result of switching from the series-parallelmode to the series mode, so the rotation speed of the electric oil pumpis increased. On the other hand, when the rotation speed of the internalcombustion engine is higher than the rotation speed of the first rotaryelectric machine, the rotation speed of the mechanical oil pumptemporarily increases as a result of switching from the series-parallelmode to the series mode, so the rotation speed of the electric oil pumpis decreased. Thus, a temporal increase or reduction in hydraulicpressure of the mechanical oil pump resulting from switching from theseries-parallel mode to the series mode is appropriately compensated byhydraulic pressure of the electric oil pump.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the invention will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a view that shows the overall configuration of a hybridvehicle according to an embodiment that is an example of the invention;

FIG. 2 is a block diagram that schematically shows power transmissionpaths of the hybrid vehicle shown in FIG. 1;

FIG. 3 is a block diagram that shows the configuration of a controllerfor the hybrid vehicle shown in FIG. 1;

FIG. 4 is a view that schematically shows the configuration of ahydraulic circuit mounted on the hybrid vehicle shown in FIG. 1;

FIG. 5 is a chart that shows each drive mode in the hybrid vehicle and acontrolled status of a transmission unit (power transmission unit);

FIG. 6 is a nomograph in one-motor EV mode that is one of the drivemodes shown in FIG. 5;

FIG. 7 is a nomograph in two-motor EV mode that is one of the drivemodes shown in FIG. 5;

FIG. 8 is a first nomograph in series-parallel HV mode that is one ofthe drive modes shown in FIG. 5;

FIG. 9 is a nomograph in series HV mode that is one of the drive modesshown in FIG. 5;

FIG. 10 is a time chart that shows changes in the states of the hybridvehicle at the time of switching from series-parallel mode to seriesmode among the drive modes shown in FIG. 5;

FIG. 11 is a first nomograph that shows an example of changes in thestatuses of rotating elements at the time of switching from seriesparallel mode to series mode among the drive modes shown in FIG. 5;

FIG. 12 is a second nomograph that shows an example of changes in thestatuses of the rotating elements at the time of switching fromseries-parallel mode to series mode among the drive modes shown in FIG.5; and

FIG. 13 is a second nomograph in series-parallel HV mode that is one ofthe drive modes shown in FIG. 5.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the invention will be described withreference to the accompanying drawings. Like reference numerals denotethe same or corresponding portions in the following embodiment, and thedescription thereof will not be repeated.

Initially, the overall configuration of a hybrid vehicle will bedescribed. FIG. 1 is a view that shows the overall configuration of ahybrid vehicle (which may be simply referred to as vehicle) 1 accordingto the embodiment that is an example of the invention. The hybridvehicle 1 includes an engine 10, a drive system 2, drive wheels 90 and acontroller 100. The drive system 2 includes a first motor generator(hereinafter, referred to as first MG) 20 that is a first rotaryelectric machine, a second motor generator (hereinafter, referred to assecond MG) 30 that is a second rotary electric machine, a transmissionunit (power transmission unit) 40, a differential unit 50, a clutch CS,an input shaft 21, a counter shaft 70 that is an output shaft of thedrive system 2, a differential gear set 80 and a hydraulic circuit 500.

The vehicle 1 is a front-engine front-drive (FF) hybrid vehicle thattravels by using the power of at least any one of the engine 10, thefirst MG 20 and the second MG 30. The vehicle 1 may be a plug-in hybridvehicle of which a battery (see FIG. 2) 60 is rechargeable from anexternal power supply.

The engine 10 is, for example, an internal combustion engine, such as agasoline engine and a diesel engine. Each of the first MG 20 and thesecond MG 30 is, for example, a permanent magnet synchronous motor thatincludes a rotor in which permanent magnets are embedded. The drivesystem 2 is a double-axis drive system in which the first MG 20 isprovided along a first axis 12 coaxial with the crankshaft of the engine10 and the second MG 30 is provided along a second axis 14 differentfrom the first axis 12. The first axis 12 and the second axis 14 areparallel to each other.

The transmission unit 40, the differential unit 50 and the clutch CS arefurther provided along the first axis 12. The transmission unit 40, thedifferential unit 50, the first MG 20 and the clutch CS are arrangedfrom the side close to the engine 10 in the stated order.

The first MG 20 is provided so as to be able to receive power from theengine 10. More specifically, the input shaft 21 of the drive system 2is connected to the crankshaft of the engine 10. The input shaft 21extends along the first axis 12 in a direction away from the engine 10.The input shaft 21 is connected to the clutch CS at its distal endextending from the engine 10. A rotary shaft 22 of the first MG 20extends in a cylindrical shape along the first axis 12. The input shaft21 passes through the inside of the rotary shaft 22 at a portion beforethe input shaft 21 is connected to the clutch CS. The input shaft 21 isconnected to the rotary shaft 22 of the first MG 20 via the clutch CS.

The clutch CS is a hydraulic friction engagement element that is able tocouple the input shaft 21 to the rotary shaft 22 of the first MG 20.When the clutch CS is placed in an engaged state, the input shaft 21 andthe rotary shaft 22 are coupled to each other, and the power of theengine 10 is allowed to be directly transmitted to the first MG 20 viathe clutch CS. On the other hand, when the clutch CS is placed in areleased state, coupling of the input shaft 21 to the rotary shaft 22 isreleased, and the power of the engine 10 is not allowed to be directlytransmitted to the first MG 20 via the clutch CS.

The transmission unit 40 shifts power from the engine 10 and thenoutputs the power to the differential unit 50. The transmission unit 40includes a single-pinion-type planetary gear mechanism, a clutch C1 anda brake B1. The single-pinion-type planetary gear mechanism includes asun gear S1, pinions P1, a ring gear R1 and a carrier CA1.

The sun gear S1 is provided such that the rotation center of the sungear S1 coincides with the first axis 12. The ring gear R1 is providedcoaxially with the sun gear S1 on the radially outer side of the sungear S1. The pinions P1 are arranged between the sun gear S1 and thering gear R1, and are in mesh with the sun gear S1 and the ring gear R1.The pinions P1 are rotatably supported by the carrier CA1. The carrierCA1 is connected to the input shaft 21, and rotates integrally with theinput shaft 21. Each of the pinions P1 is provided so as to berevolvable about the first axis 12 and rotatable around the central axisof the pinion P1.

As will be described later, the rotation speed of the sun gear S1, therotation speed of the carrier CA1 (that is, the rotation speed of theengine 10) and the rotation speed of the ring gear R1 are in therelationship represented by points that are connected by a straight linein each of the nomographs (that is, the relationship that, when any tworotation speeds are determined, the remaining one rotation speed is alsodetermined).

In the present embodiment, the carrier CA1 is provided as an inputelement to which power is input from the engine 10, and the ring gear R1is provided as an output element that outputs the power input to thecarrier CA1. By the use of the planetary gear mechanism including thesun gear S1, the pinions P1, the ring gear R1 and the carrier CA1, powerinput to the carrier CA1 is shifted and output from the ring gear R1.

The clutch C1 is a hydraulic friction engagement element that is able tocouple the sun gear S1 to the carrier CA1. When the clutch C1 is placedin an engaged state, the sun gear S1 and the carrier CA1 rotateintegrally with each other. When the clutch C1 is placed in a releasedstate, integral rotation of the sun gear S1 and the carrier CA1 iscancelled.

The brake B1 is a hydraulic friction engagement element that is able torestrict (lock) the rotation of the sun gear S1. When the brake B1 isplaced in an engaged state, the sun gear S1 is fixed to the case body ofthe drive system, and the rotation of the sun gear S1 is restricted.When the brake B1 is placed in a released state (disengaged state), thesun gear S1 is separated from the case body of the drive system, and therotation of the sun gear S1 is allowed.

A speed ratio (the ratio of the rotation speed of the carrier CA1 thatis the input element to the rotation speed of the ring gear R1 that isthe output element, specifically, Rotation Speed of Carrier CA1/RotationSpeed of Ring Gear R1) of the transmission unit 40 is changed inresponse to a combination of the engaged/released states of the clutchC1 and brake B1. When the clutch C1 is engaged and the brake B1 isreleased, a low gear position Lo in which the speed ratio is 1.0(directly coupled state) is established. When the clutch C1 is releasedand the brake B1 is engaged, a high gear position Hi in which the speedratio is smaller than 1.0 (for example, 0.7, and a so-called over-drivestate) is established. When the clutch C1 is engaged and the brake B1 isengaged, the rotation of the sun gear S1 and the rotation of the carrierCA1 are restricted, so the rotation of the ring gear R1 is alsorestricted.

The transmission unit 40 is configured to be able to switch between anon-neutral state and a neutral state. In the non-neutral state, poweris transmitted. In the neutral state, power is not transmitted. In thepresent embodiment, the above-described directly coupled state andover-drive state correspond to the non-neutral state. On the other hand,when both the clutch C1 and the brake B1 are released, the carrier CA1is allowed to coast about the first axis 12. Thus, the neutral state inwhich power transmitted from the engine 10 to the carrier CA1 is nottransmitted from the carrier CA1 to the ring gear R1 is obtained.

The differential unit 50 includes a single-pinion-type planetary gearmechanism and a counter drive gear 51. The single-pinion-type planetarygear mechanism includes a sun gear S2, pinions P2, a ring gear R2 and acarrier CA2.

The sun gear S2 is provided such that the rotation center of the sungear S2 coincides with the first axis 12. The ring gear R2 is providedcoaxially with the sun gear S2 on the radially outer side of the sungear S2. The pinions P2 are arranged between the sun gear S2 and thering gear R2, and are in mesh with the sun gear S2 and the ring gear R2.The pinions P2 are rotatably supported by the carrier CA2. The carrierCA2 is connected to the ring gear R1 of the transmission unit 40, androtates integrally with the ring gear R1. Each of the pinions P2 isprovided so as to be revolvable about the first axis 12 and rotatablearound the central axis of the pinion P2.

The rotary shaft 22 of the first MG 20 is connected to the sun gear S2.The rotary shaft 22 of the first MG 20 rotates integrally with the sungear S2. The counter drive gear 51 is connected to the ring gear R2. Thecounter drive gear 51 is an output gear of the differential unit 50. Theoutput gear rotates integrally with the ring gear R2.

As will be described later, the rotation speed of the sun gear S2 (thatis, the rotation speed of the first MG 20), the rotation speed of thecarrier CA2 and the rotation speed of the ring gear R2 are in therelationship represented by points that are connected by a straight linein each of the nomographs (that is, the relationship that, when any tworotation speeds are determined, the remaining one rotation speed is alsodetermined). Therefore, when the rotation speed of the carrier CA2 is apredetermined value, it is possible to steplessly change the rotationspeed of the ring gear R2 by adjusting the rotation speed of the firstMG 20.

The counter shaft 70 extends parallel to the first axis 12 and thesecond axis 14. The counter shaft 70 is arranged parallel to the rotaryshaft 22 of the first MG 20 and a rotary shaft 31 of the second MG 30. Adriven gear 71 and a drive gear 72 are provided on the counter shaft 70.The driven gear 71 is in mesh with the counter drive gear 51 of thedifferential unit 50. That is, the power of the engine 10 and the powerof the first MG 20 are transmitted to the counter shaft 70 via thecounter drive gear 51 of the differential unit 50.

The transmission unit 40 and the differential unit 50 are connected inseries with each other in a power transmission path from the engine 10to the counter shaft 70. Therefore, power from the engine 10 is shiftedin the transmission unit 40 and the differential unit 50 and thentransmitted to the counter shaft 70.

The driven gear 71 is in mesh with a reduction gear 32 connected to therotary shaft 31 of the second MG 30. That is, the power of the second MG30 is transmitted to the counter shaft 70 via the reduction gear 32.

The drive gear 72 is in mesh with a differential ring gear 81 of thedifferential gear set 80. The differential gear set 80 is connected tothe right and left drive wheels 90 via corresponding right and leftdrive shafts 82. That is, the rotation of the counter shaft 70 istransmitted to the right and left drive shafts 82 via the differentialgear set 80.

With the above-described configuration in which the clutch CS isprovided, the hybrid vehicle 1 is allowed to operate in a mode in whicha series-parallel system is used (hereinafter, referred to asseries-parallel mode) and is also allowed to operate in a mode in whicha series system is used (hereinafter, referred to as series mode). Interms of this point, how power is transmitted from the engine in eachmode will be described with reference to the schematic view shown inFIG. 2.

FIG. 2 is a block diagram that schematically shows power transmissionpaths of components of the hybrid vehicle shown in FIG. 1. The hybridvehicle 1 includes the engine 10, the first MG 20, the second MG 30, thetransmission unit 40, the differential unit 50, the battery 60 and theclutch CS. The battery 60 supplies electric power to the first MG 20 orthe second MG 30 during motoring of a corresponding one of the first MG20 and the second MG 30, and stores electric power generated by thefirst MG 20 or the second MG 30 during regeneration of a correspondingone of the first MG 20 and the second MG 30.

The hybrid vehicle 1 includes two paths K1, K2 as a path through whichthe power of the engine 10 is transmitted to the first MG 20.

The path K1 is a path through which the power of the engine 10 istransmitted to the first MG 20 via the transmission unit 40 and thedifferential unit 50. When the transmission unit 40 is placed in anon-neutral state (any one of the clutch C1 and the brake B1 is placedin the engaged state, and the other one of the clutch C1 and the brakeB1 is placed in the released state), the power of the engine 10 istransmitted to the first MG 20 through the path K1. On the other hand,when the transmission unit 40 is placed in a neutral state (both theclutch C1 and the brake B1 are placed in the released state),transmission of power through the path K1 is interrupted.

The path K2 is different from the path K1, and is a path through whichthe power of the engine 10 is directly transmitted to the first MG 20without passing through the transmission unit 40 or the differentialunit 50. The clutch CS is provided in the path K2. When the clutch CS isplaced in the engaged state, the power of the engine 10 is transmittedto the first MG 20 through the path K2. On the other hand, when theclutch CS is placed in the released state, transmission of power throughthe path K2 is interrupted.

In HV mode in which the engine 10 is operated, when the power of theengine 10 is transmitted through the path K1 and the path K2 isinterrupted (that is, the transmission unit 40 is placed in thenon-neutral state and the clutch CS is placed in the released state),the hybrid vehicle 1 is operable in series-parallel mode.

On the other hand, in HV mode in which the engine 10 is operated, whenthe power of the engine 10 is transmitted through the path K2 and thepath K1 is interrupted (that is, the transmission unit 40 is placed inthe neutral state and the clutch CS is placed in the engaged state), thehybrid vehicle 1 is operable in series mode. At this time, in thedifferential unit 50, the carrier CA2 connected to the transmission unit40 is freely rotatable (free), so the sun gear S2 connected to the firstMG 20 and the ring gear R2 connected to the second MG 30 do notinfluence each other and are rotatable. Therefore, it is possible toindependently perform the operation of generating electric power byrotating the first MG 20 with the use of the rotation of the engine 10and the operation of rotating the drive wheels by driving the second MG30.

The transmission unit 40 does not always need to be able to change thespeed ratio. As long as it is possible to interrupt transmission ofpower through the path K1, a mere clutch is applicable.

The configuration of the controller will be described below. FIG. 3 is ablock diagram that shows the configuration of the controller 100 of thehybrid vehicle 1 shown in FIG. 1. The controller 100 includes an HV ECU150, an MG ECU 160 and an engine ECU 170. Each of the HV ECU 150, the MGECU 160 and the engine ECU 170 is an electronic control unit including acomputer. The number of ECUs is not limited to three. An integratedsingle ECU may be provided as a whole, or two or four or more of dividedECUs may be provided.

The MG ECU 160 controls the first MG 20 and the second MG 30. The MG ECU160, for example, controls the output torque of the first MG 20 byadjusting the value of current that is supplied to the first MG 20. TheMG ECU 160 controls the output torque of the second MG 30 by adjustingthe value of current that is supplied to the second MG 30.

The engine ECU 170 controls the engine 10. The engine ECU 170, forexample, controls the opening degree of an electronic throttle valve ofthe engine 10, controls ignition of the engine by outputting an ignitionsignal, or controls injection of fuel to the engine 10. The engine ECU170 controls the output torque of the engine 10 through opening degreecontrol over the electronic throttle valve, injection control, ignitioncontrol, and the like.

The HV ECU 150 comprehensively controls the entire vehicle. A vehiclespeed sensor, an accelerator operation amount sensor, an MG1 rotationspeed sensor, an MG2 rotation speed sensor, an output shaft rotationspeed sensor, a battery sensor, and the like, are connected to the HVECU 150. With these sensors, the HV ECU 150 acquires a vehicle speed, anaccelerator operation amount, the rotation speed of the first MG 20, therotation speed of the second MG 30, the rotation speed of the outputshaft of a power transmission system, a battery state SOC, and the like.

The HV ECU 150 calculates a required driving force, a required power, arequired torque, and the like, for the vehicle based on acquiredinformation. The HV ECU 150 determines the output torque of the first MG20 (hereinafter, also referred to as MG1 torque), the output torque ofthe second MG 30 (hereinafter, also referred to as MG2 torque) and theoutput torque of the engine 10 (hereinafter, also referred to as enginetorque) based on the calculated required values. The HV ECU 150 outputsa command value of the MG1 torque and a command value of the MG2 torqueto the MG ECU 160. The HV ECU 150 outputs a command value of the enginetorque to the engine ECU 170.

The HV ECU 150 controls the clutches C1, CS and the brake B1 based onthe drive mode (described later), and the like. The HV ECU 150 outputs,to the hydraulic circuit 500 shown in FIG. 1, a command value (PbC1) ofhydraulic pressure that is supplied to the clutch C1, a command value(PbCS) of hydraulic pressure that is supplied to the clutch CS and acommand value (PbB1) of hydraulic pressure that is supplied to the brakeB1.

The HV ECU 150 outputs a control signal NM for controlling an electricoil pump 502 (see FIG. 4 (described later)) and a control signal S/C forcontrolling an electromagnetic switching valve 560 (see FIG. 4(described later)) to the hydraulic circuit 500 shown in FIG. 1.

Next, the configuration of the hydraulic circuit will be described. FIG.4 is a view that schematically shows the configuration of the hydrauliccircuit 500 mounted on the hybrid vehicle 1. The hydraulic circuit 500includes a mechanical oil pump (hereinafter, also referred to as MOP)501, the electric oil pump (hereinafter, also referred to as EOP) 502,pressure regulating valves 510, 520, linear solenoid valves SL1, SL2,SL3, simultaneous supply prevention valves 530, 540, 550, anelectromagnetic change-over valve 560, a check valve 570, and oilpassages LM, LE, L1, L2, L3, L4.

The MOP 501 is connected to the carrier CA2 among the three rotatingelements (sun gear S2, ring gear R2, carrier CA2) that constitute thedifferential unit 50. More specifically, as shown in FIG. 1, the MOP 501is connected to the carrier CA2 via a plurality of gears 506, 507. Thegear 506 is connected to the carrier CA2 of the differential unit 50,and rotates integrally with the carrier CA2 around a first axis 12. Thegear 507 is provided on the radially outer side of the gear 506, and isin mesh with the gear 506. A rotary shaft 508 of the gear 507 isconnected to a drive shaft of the MOP 501 arranged coaxially with therotary shaft 508. With the above configuration, rotation of the carrierCA2 of the differential unit 50 is transmitted to the drive shaft of theMOP 501 through the gear 506 and the gear 507.

The MOP 501 is operated by power that is transmitted from the carrierCA2 of the differential unit 50 to generate hydraulic pressure.Therefore, when the carrier CA2 is rotated, the MOP 501 is alsooperated; whereas, when the carrier CA2 is stopped, the MOP 501 is alsostopped. The MOP 501 outputs generated hydraulic pressure to the oilpassage LM.

One of the most characteristic points of the hydraulic circuit 500according to the present embodiment is that the MOP 501 is connected tonot the carrier CA1 of the transmission unit 40 but the carrier CA2 ofthe differential unit 50. Thus, it is possible to operate the MOP 501even in a state where rotation of the carrier CA1 of the transmissionunit 40 is stopped as a result of a stop of the engine 10. This pointwill be described in detail later.

The hydraulic pressure in the oil passage LM is regulated (reduced) to apredetermined pressure by the pressure regulating valve 510.Hereinafter, the hydraulic pressure in the oil passage LM, regulated bythe pressure regulating valve 510, is also referred to as line pressurePL. The line pressure PL is supplied to each of the linear solenoidvalves SL1, SL2, SL3.

The linear solenoid valve SL1 generates hydraulic pressure for engagingthe clutch C1 (hereinafter, referred to as C1 pressure) by regulatingthe line pressure PL in response to the hydraulic pressure command valuePbC1 from the controller 100. The C1 pressure is supplied to the clutchC1 via the oil passage L1.

The linear solenoid valve SL2 generates hydraulic pressure for engagingthe brake B1 (hereinafter, referred to as B1 pressure) by regulating theline pressure PL in response to the hydraulic pressure command valuePbB1 from the controller 100. The B1 pressure is supplied to the brakeB1 via the oil passage L2.

The linear solenoid valve SL3 generates hydraulic pressure for engagingthe clutch CS (hereinafter, referred to as CS pressure) by regulatingthe line pressure PL in response to the hydraulic pressure command valuePbCS from the controller 100. The CS pressure is supplied to the clutchCS via the oil passage L3.

The simultaneous supply prevention valve 530 is provided in the oilpassage L1, and is configured to prevent the clutch C1 and at least oneof the brake B1 and the clutch CS from being simultaneously engaged.Specifically, the oil passages L2, L3 are connected to the simultaneoussupply prevention valve 530. The simultaneous supply prevention valve530 operates by using the B1 pressure and the CS pressure through theoil passages L2, L3 as signal pressures.

When both signal pressures that are the B1 pressure and the CS pressureare not input to the simultaneous supply prevention valve 530 (that is,when both the brake B1 and the clutch CS are released), the simultaneoussupply prevention valve 530 is in a normal state in which the C1pressure is supplied to the clutch C1. FIG. 4 illustrates the case wherethe simultaneous supply prevention valve 530 is in the normal state.

On the other hand, when at least one of the signal pressures that arethe B1 pressure and the CS pressure is input to the simultaneous supplyprevention valve 530 (that is, when at least one of the brake B1 and theclutch CS is engaged), even when the clutch C1 is engaged, thesimultaneous supply prevention valve 530 switches into a drain state inwhich supply of the C1 pressure to the clutch C1 is cut off and thehydraulic pressure in the clutch C1 is released to the outside. Thus,the clutch C1 is released, so the clutch C1 and at least one of thebrake B1 and the clutch CS are prevented from being simultaneouslyengaged.

Similarly, the simultaneous supply prevention valve 540 operates inresponse to the C1 pressure and the CS pressure as signal pressures toprevent the brake B1 and at least one of the clutch C1 and the clutch CSfrom being simultaneously engaged. Specifically, when both the signalpressures that are the C1 pressure and the CS pressure are not input tothe simultaneous supply prevention valve 540, the simultaneous supplyprevention valve 540 is in a normal state in which the B1 pressure issupplied to the brake B1. On the other hand, when at least one of thesignal pressures that are the C1 pressure and the CS pressure is inputto the simultaneous supply prevention valve 540, the simultaneous supplyprevention valve 540 switches into a drain state in which supply of theB1 pressure to the brake B1 is cut off and the hydraulic pressure in thebrake B1 is released to the outside. FIG. 4 illustrates the case wherethe C1 pressure is input to the simultaneous supply prevention valve 540as the signal pressure and the simultaneous supply prevention valve 540is in the drain state.

Similarly, the simultaneous supply prevention valve (hydraulic valve)550 operates by using the C1 pressure and the B1 pressure as signalpressures to prevent the clutch CS and at least one of the clutch C1 andthe brake B1 from being simultaneously engaged. Specifically, when boththe signal pressures that are the C1 pressure and the B1 pressure arenot input to the simultaneous supply prevention valve 550, thesimultaneous supply prevention valve 550 is in a normal state in whichthe CS pressure is supplied to the clutch CS. On the other hand, when atleast one of the signal pressures that are the C1 pressure and the B1pressure is input to the simultaneous supply prevention valve 550, thesimultaneous supply prevention valve 550 switches into a drain state inwhich supply of the CS pressure to the clutch CS is cut off and thehydraulic pressure in the clutch CS is released to the outside. FIG. 4illustrates the case where the C1 pressure is input to the simultaneoussupply prevention valve 550 and the simultaneous supply prevention valve550 is in the drain state.

The EOP 502 is driven by a motor 502A to generate hydraulic pressure.The motor 502A is controlled by the control signal NM from thecontroller 100. Therefore, the EOP 502 is operable irrespective ofwhether the carrier CA2 is rotating. The EOP 502 outputs generatedhydraulic pressure to the oil passage LE.

The hydraulic pressure in the oil passage LE is regulated (reduced) to apredetermined pressure by the pressure regulating valve 520. The oilpassage LE is connected to the oil passage LM via the check valve 570.When the hydraulic pressure in the oil passage LE is higher by apredetermined pressure or more than the hydraulic pressure in the oilpassage LM, the check valve 570 opens, and the hydraulic pressure in theoil passage LE is supplied to the oil passage LM via the check valve570. Thus, during a stop of the MOP 501 as well, it is possible tosupply hydraulic pressure to the oil passage LM by driving the EOP 502.

The electromagnetic change-over valve 560 is switched to any one of anon state and an off state in response to the control signal S/C from thecontroller 100. In the on state, the electromagnetic change-over valve560 communicates the oil passage LE with the oil passage L4. In the offstate, the electromagnetic change-over valve 560 interrupts the oilpassage LE from the oil passage L4, and releases the hydraulic pressurein the oil passage L4 to the outside. FIG. 4 illustrates the case wherethe electromagnetic change-over valve 560 is in the off state.

The oil passage L4 is connected to the simultaneous supply preventionvalves 530, 540. When the electromagnetic change-over valve 560 is inthe on state, the hydraulic pressure in the oil passage LE is input tothe simultaneous supply prevention valves 530, 540 via the oil passageL4 as a signal pressure. When the signal pressure from the oil passageL4 is input to the simultaneous supply prevention valve 530, thesimultaneous supply prevention valve 530 is forcibly fixed to the normalstate irrespective of whether the signal pressure (B1 pressure) is inputfrom the oil passage L2. Similarly, when the signal pressure is inputfrom the oil passage L4 to the simultaneous supply prevention valve 540,the simultaneous supply prevention valve 540 is forcibly fixed to thenormal state irrespective of whether the signal pressure (C1 pressure)is input from the oil passage L1. Therefore, by driving the EOP 502 andswitching the electromagnetic change-over valve 560 to the on state, thesimultaneous supply prevention valves 530, 540 are simultaneously fixedto the normal state. Thus, the clutch C1 and the brake B1 are allowed tobe simultaneously engaged, and two-motor mode (described later) isenabled.

Next, control modes of the hybrid vehicle 1 will be described.Hereinafter, the details of the control modes of the hybrid vehicle 1will be described with reference to an operation engagement chart andthe nomographs.

FIG. 5 is a chart that shows each drive mode and controlled statuses ofthe clutch C1 and brake B1 of the transmission unit (power transmissionunit) 40 in each drive mode.

The controller 100 causes the hybrid vehicle 1 to travel in motor drivemode (hereinafter, referred to as EV mode) or hybrid mode (hereinafter,referred to as HV mode). The EV mode is a control mode in which theengine 10 is stopped and the hybrid vehicle 1 is caused to travel byusing the power of at least one of the first MG 20 and the second MG 30.The HV mode is a control mode in which the hybrid vehicle 1 is caused totravel by using the power of the engine 10 and the power of the secondMG 30. Each of the EV mode and the HV mode is further divided into somecontrol modes.

In FIG. 5, C1, B1, CS, MG1 and MG2, respectively denote the clutch C1,the brake B1, the clutch CS, the first MG 20 and the second MG 30. Thecircle mark (◯) in each of the C1, B1, CS columns indicates the engagedstate, the cross mark (×) indicates the released state, and the trianglemark (Δ) indicates that any one of the clutch C1 and the brake B1 isengaged during engine brake. The sign G in each of the MG1 column andthe MG2 column indicates that the MG1 or the MG2 is mainly operated as agenerator. The sign M in each of the MG1 column and the MG2 columnindicates that the MG1 or the MG2 is mainly operated as a motor.

In EV mode, the controller 100 selectively switches between one-motormode and two-motor mode in response to a user's required torque, and thelike. In one-motor mode, the hybrid vehicle 1 is caused to travel byusing the power of the second MG 30 alone. In two-motor mode, the hybridvehicle 1 is caused to travel by using the power of both the first MG 20and the second MG 30. For example, when the load of the drive system 2is low, the one-motor mode is used, and, when the load of the drivesystem 2 becomes high, the drive mode is changed to the two-motor mode.

As shown in E1 line of FIG. 5, when the hybrid vehicle 1 is driven(moved forward or reversed) in one-motor EV mode, the controller 100places the transmission unit 40 in the neutral state (state in which nopower is transmitted) by releasing the clutch C1 and releasing the brakeB1. At this time, the controller 100 mainly uses the first MG 20 to fixthe rotation speed of the sun gear S2 to zero, and causes the second MG30 to operate as a motor (see FIG. 6 (described later)). As a techniquefor fixing the rotation speed of the sun gear S2 to zero with the use ofthe first MG 20, the current of the first MG 20 may be controlled in afeedback manner such that the rotation speed of the first MG 20 becomeszero or, if possible, cogging torque of the first MG 20 may be utilizedwithout adding current to the first MG 20. When the transmission unit 40is placed in the neutral state, the engine 10 is not co-rotated duringbraking, so a loss is smaller by that amount, and it is possible torecover large regenerated electric power.

As shown in the E2 line in FIG. 5, when the hybrid vehicle 1 is brakedin one-motor EV mode and engine brake is required, the controller 100engages any one of the clutch C1 and the brake B1. For example, whenbraking force is insufficient with only regenerative brake, engine brakeis used together with regenerative brake. For example, when the SOC ofthe battery is close to a full charge state, regenerated electric powercannot be charged, so it is conceivable to establish an engine brakestate.

By engaging any one of the clutch C1 and the brake B1, a so-calledengine brake state is established. In the engine brake state, therotation of the drive wheels 90 is transmitted to the engine 10, and theengine 10 is rotated. At this time, the controller 100 causes the firstMG 20 to mainly operate as a motor, and causes the second MG 30 tomainly operate as a generator.

On the other hand, as shown in the E3 line in FIG. 5, when the hybridvehicle 1 is driven (moved forward or reversed) in two-motor EV mode,the controller 100 restricts (locks) the rotation of the ring gear R1 ofthe transmission unit 40 by engaging the clutch C1 and engaging thebrake B1. Thus, the rotation of the carrier CA2 of the differential unit50 coupled to the ring gear R1 of the transmission unit 40 is alsorestricted (locked), so the carrier CA2 of the differential unit 50 iskept in a stopped state (Engine Rotation Speed Ne=0). The controller 100causes the first MG 20 and the second MG 30 to mainly operate as motors(see FIG. 7 (described later)).

In EV mode (one-motor mode or two-motor mode), the engine 10 is stopped,so the MOP 501 is also stopped. Therefore, in EV mode, the clutch C1 orthe brake B1 is engaged by using hydraulic pressure that is generated bythe EOP 502.

In HV mode, the controller 100 causes the first MG 20 to operate as agenerator, and causes the second MG 30 to operate as a motor. In HVmode, the controller 100 sets the control mode to any one of theseries-parallel mode and the series mode.

In series-parallel mode, part of the power of the engine 10 is used inorder to drive the drive wheels 90, and the remaining part of the powerof the engine 10 is used as power for generating electric power in thefirst MG 20. The second MG 30 drives the drive wheels 90 by usingelectric power generated by the first MG 20. In series-parallel mode,the controller 100 changes the speed ratio of the transmission unit 40in response to the vehicle speed.

When the hybrid vehicle 1 is caused to move forward in an intermediateor low speed range, the controller 100 establishes the low gear positionLo (see the continuous line in FIG. 8 (described later)) by engaging theclutch C1 and releasing the brake B1 as shown in the H2 line in FIG. 5.On the other hand, when the hybrid vehicle 1 is caused to move forwardin a high speed range, the controller 100 establishes the high gearposition Hi (see the dashed line in FIG. 8 (described later)) byreleasing the clutch C1 and engaging the brake B1 as shown in the H1line in FIG. 5. Either when the high gear position is established orwhen the low gear position is established, the transmission unit 40 andthe differential unit 50 operate as a continuously variable transmissionas a whole.

When the hybrid vehicle 1 is reversed, the controller 100 engages theclutch C1 and releases the brake B1 as shown in the H3 line in FIG. 5.When there is an allowance in the SOC of the battery, the controller 100rotates the second MG 30 alone in the reverse direction; whereas, whenthere is no allowance in the SOC of the battery, the controller 100generates electric power with the use of the first MG 20 by operatingthe engine 10 and rotates the second MG 30 in the reverse direction.

In series mode, the entire power of the engine 10 is used as power forgenerating electric power with the use of the first MG 20. The second MG30 drives the drive wheels 90 by using electric power generated by thefirst MG 20. In series mode, when the hybrid vehicle 1 is moved forwardor when the hybrid vehicle 1 is reversed, the controller 100 releasesboth the clutch C1 and the brake B1 and engages the clutch CS (see FIG.9 (described later)) as shown in the H4 line and the H5 line in FIG. 5.

In HV mode, the engine 10 is operating, so the MOP 501 is alsooperating. Therefore, in HV mode, the clutch C1, the clutch CS or thebrake B1 is engaged mainly by using hydraulic pressure generated by theMOP 501.

Hereinafter, the statuses of the rotating elements in each operationmode shown in FIG. 5 will be described with reference to the nomographs.

FIG. 6 is a nomograph in one-motor EV mode. FIG. 7 is a nomograph intwo-motor EV mode. FIG. 8 is a nomograph in series-parallel mode. FIG. 9is a nomograph in series mode.

In FIG. 6 to FIG. 9, S1, CA1 and R1 respectively denote the sun gear S1,the carrier CA1 and the ring gear R1 of the transmission unit 40, S2,CA2 and R2 respectively denote the sun gear S2, the carrier CA2 and thering gear R2 of the differential unit 50.

The controlled status in one-motor EV mode (E1 line in FIG. 5) will bedescribed with reference to FIG. 6. In one-motor EV mode, the controller100 releases the clutch C1, the brake B1 and the clutch CS of thetransmission unit 40, stops the engine 10, and causes the second MG 30to mainly operate as a motor. Therefore, in one-motor EV mode, thehybrid vehicle 1 travels by using the torque of the second MG 30(hereinafter, referred to as second MG torque Tm2).

At this time, the controller 100 executes feedback control over thetorque of the first MG 20 (hereinafter, referred to as first MG torqueTm1) such that the rotation speed of the sun gear S2 becomes zero.Therefore, the sun gear S2 does not rotate. However, because the clutchC1 and brake B1 of the transmission unit 40 are released, the rotationof the carrier CA2 of the differential unit 50 is not restricted.Therefore, the ring gear R2 and carrier CA2 of the differential unit 50and the ring gear R1 of the transmission unit 40 are rotated (coasted)interlocking with the rotation of the second MG 30 in the same directionas the second MG 30.

On the other hand, the carrier CA1 of the transmission unit 40 is keptin a stopped state because the engine 10 is stopped. The sun gear S1 ofthe transmission unit 40 is rotated (coasted) interlocking with therotation of the ring gear R1 in a direction opposite to the rotationdirection of the ring gear R1.

In order to decelerate the vehicle in one-motor EV mode, it is allowedto activate engine brake in addition to regenerative brake using thesecond MG 30. In this case (E2 line in FIG. 5), by engaging any one ofthe clutch C1 and the brake B1, the engine 10 is also rotated at thetime when the carrier CA2 is driven from the drive wheels 90 side, soengine brake is activated.

Next, the controlled status in two-motor EV mode (E3 line in FIG. 5)will be described with reference to FIG. 7. In two-motor EV mode, thecontroller 100 engages the clutch C1 and the brake B1, releases theclutch CS, and stops the engine 10. Therefore, the rotation of each ofthe sun gear S1, carrier CA1 and ring gear R1 of the transmission unit40 is restricted such that the rotation speed becomes zero.

Because the rotation of the ring gear R1 of the transmission unit 40 isrestricted, the rotation of the carrier CA2 of the differential unit 50is also restricted (locked). In this state, the controller 100 causesthe first MG 20 and the second MG 30 to mainly operate as motors.Specifically, the second MG 30 is rotated in the positive direction bysetting the second MG torque Tm2 to a positive torque, and the first MG20 is rotated in the negative direction by setting the first MG torqueTm1 to a negative torque.

When the rotation of the carrier CA2 is restricted by engaging theclutch C1, the first MG torque Tm1 is transmitted to the ring gear R2 byusing the carrier CA2 as a supporting point. The first MG torque Tm1(hereinafter, referred to as first MG transmission torque Tm1 c) that istransmitted to the ring gear R2 acts in the positive direction, and istransmitted to the counter shaft 70. Therefore, in two-motor EV mode,the hybrid vehicle 1 travels by using the first MG transmission torqueTm1 c and the second MG torque Tm2. The controller 100 adjusts thedistribution ratio between the first MG torque Tm1 and the second MGtorque Tm2 such that the sum of the first MG transmission torque Tm1 cand the second MG torque Tm2 meets the user's required torque.

The controlled state in series-parallel HV mode (H1 to H3 lines in FIG.5) will be described with reference to FIG. 8. FIG. 8 illustrates thecase where the vehicle is traveling forward in the low gear position Lo(see H2 line in FIG. 5, and the continuous common line shown in thenomograph of S1, CA1 and R1 in FIG. 8) and the case where the vehicle istraveling forward in the high gear position Hi (see H1 line in FIG. 5,and the dashed common line shown in the nomograph of S1, CA1 and R1 inFIG. 8). For the sake of convenience of description, it is assumed thatthe rotation speed of the ring gear R1 is the same either when thevehicle is traveling forward in the low gear position Lo or when thevehicle is traveling forward in the high gear position Hi.

When the low gear position Lo is established in series-parallel HV mode,the controller 100 engages the clutch C1, and releases the brake B1 andthe clutch CS. Therefore, the rotating elements (the sun gear S1, thecarrier CA1 and the ring gear R1) rotate integrally with one another.Thus, the ring gear R1 of the transmission unit 40 also rotates at thesame rotation speed as the carrier CA1, and the rotation of the engine10 is transmitted from the ring gear R1 to the carrier CA2 of thedifferential unit 50 at the same rotation speed. That is, the torque ofthe engine 10 (hereinafter, referred to as engine torque Te) input tothe carrier CA1 of the transmission unit 40 is transmitted from the ringgear R1 of the transmission unit 40 to the carrier CA2 of thedifferential unit 50. When the low gear position Lo is established, thetorque that is transmitted from the ring gear R1 (hereinafter, referredto as transmission unit output torque Tr1) is equal to the engine torqueTe (Te=Tr1).

The rotation of the engine 10, transmitted to the carrier CA2 of thedifferential unit 50, is steplessly shifted by the use of the rotationspeed of the sun gear S2 (the rotation speed of the first MG 20), and istransmitted to the ring gear R2 of the differential unit 50. At thistime, the controller 100 basically causes the first MG 20 to operate asa generator to apply the first MG torque Tm1 in the negative direction.Thus, the first MG torque Tm1 serves as reaction force for transmittingthe engine torque Te, input to the carrier CA2, to the ring gear R2.

The engine torque Te transmitted to the ring gear R2 (hereinafter,referred to as engine transmission torque Tec) is transmitted from thecounter drive gear 51 to the counter shaft 70, and acts as driving forceof the hybrid vehicle 1.

In series-parallel HV mode, the controller 100 causes the second MG 30to mainly operate as a motor. The second MG torque Tm2 is transmittedfrom the reduction gear 32 to the counter shaft 70, and acts as drivingforce of the hybrid vehicle 1. That is, in series-parallel HV mode, thehybrid vehicle 1 travels by using the engine transmission torque Tec andthe second MG torque Tm2.

On the other hand, when the high gear position Hi is established inseries-parallel HV mode, the controller 100 engages the brake B1, andreleases the clutch C1 and the clutch CS. Because the brake B1 isengaged, the rotation of the sun gear S1 is restricted. Thus, therotation of the engine 10, input to the carrier CA1 of the transmissionunit 40, is increased in speed, and is transmitted from the ring gear R1of the transmission unit 40 to the carrier CA2 of the differential unit50. Therefore, when the high gear position Hi is established, thetransmission unit output torque Tr1 is smaller than the engine torque Te(Te>Tr1).

The controlled statuses in series HV mode (H4 line in FIG. 5) will bedescribed with reference to FIG. 9. In series HV mode, the controller100 releases the clutch C1 and the brake B1, and engages the clutch CS.Therefore, when the clutch CS is engaged, the sun gear S2 of thedifferential unit 50 rotates at the same rotation speed as the carrierCA1 of the transmission unit 40, and the rotation of the engine 10 isdirectly transmitted to the first MG 20 via the clutch CS. Thus,electric power is allowed to be generated with the use of the first MG20 by using the engine 10 as a power source.

On the other hand, because both the clutch C1 and the brake B1 arereleased and, as a result, the transmission unit 40 is placed in theneutral state, the rotation of each of the sun gear S1 and ring gear R1of the transmission unit 40 and the rotation of the carrier CA2 of thedifferential unit 50 are not restricted. Therefore, the power of thefirst MG 20 and the power of the engine 10 are not transmitted to thecounter shaft 70. Therefore, in series HV mode, while electric power isgenerated with the use of the first MG 20 by using the engine 10 as apower source, the hybrid vehicle 1 travels by using the second MG torqueTm2 with the use of part or all of the generated electric power.

Next, the operation of the mechanical oil pump (MOP) will be described.As described above, in the hybrid vehicle 1 according to the presentembodiment, the MOP 501 is connected to the carrier CA2 of thedifferential unit 50, so it is possible to operate the MOP 501 in astate where the engine 10 is stopped.

For example, when the engine 10 is stopped during traveling in seriesmode, the rotation of the carrier CA1 of the transmission unit 40,connected to the output shaft of the engine 10; is stopped, and therotation of the sun gear S2 of the differential unit 50, coupled to thecarrier CA1 of the transmission unit 40 via the clutch CS, is alsostopped. However, when the hybrid vehicle 1 is traveling forward, thering gear R2 of the differential unit 50 is rotated, and the carrier CA2is also rotated with the rotation of the ring gear R2. Therefore, inseries mode, when the hybrid vehicle 1 is traveling forward at a vehiclespeed higher than or equal to a predetermined value, the MOP 501 isallowed to be operated even in a state where the engine 10 is stopped.

Because the MOP 501 is connected to not the sun gear S2 of thedifferential unit 50 but the carrier CA2 of the differential unit 50, itis possible to control the rotation speed of the engine 10 and therotation speed of the MOP 501 independently of each other in seriesmode.

In one-motor EV mode, the engine 10 is stopped, and the rotation of thecarrier CA1 of the transmission unit 40 is also stopped. However, byrotating the sun gear S2 with the use of the first MG 20, the carrierCA2 is allowed to be rotated irrespective of the state of the ring gearR2. That is, in one-motor EV mode, when the first MG 20 is allowed to bedriven, even when the hybrid vehicle 1 stops and the engine 10 isstopped, the MOP 501 is allowed to be operated. Therefore, it ispossible to improve the durability of the EOP 502 by reducing thefrequency of operation of the EOP 502 in one-motor EV mode.

In two-motor EV mode, as shown in FIG. 7, the rotation of thetransmission unit 40 is restricted, and the carrier CA2 of thedifferential unit 50 is also fixed, so it is not possible to operate theMOP 501. Therefore, the EOP 502 needs to be operated.

As described above, the hybrid vehicle 1 according to the presentembodiment is able to select one of the series-parallel mode and theseries mode by controlling the transmission unit 40 provided in the pathK1 and the clutch CS provided in the path K2. In addition, in the hybridvehicle 1, the MOP 501 is connected to the carrier CA2 of thedifferential unit 50. Therefore, it is possible to operate the MOP 501in a state where the engine 10 is stopped. As a result, it is possibleto improve the durability of the EOP 502 by reducing the frequency ofoperation of the EOP 502.

The carrier CA2 of the differential unit 50, to which the MOP 501 isconnected, does not rotate in the negative direction in any drive mode,so a device for preventing reverse rotation of the MOP 501 is notrequired, so the configuration around the MOP 501 is simplified. Thatis, when the MOP 501 is connected to the ring gear R2 of thedifferential unit 50, the ring gear R2 rotates in the negative directionat the time when the vehicle moves backward, so a reverse rotationprevention device (one-way clutch, or the like) for preventing reverserotation of the MOP 501 needs to be provided around the MOP 501. Whenthe MOP 501 is connected to the sun gear S2 of the differential unit 50as well, the sun gear S2 can rotate in the negative direction, so areverse rotation prevention device needs to be provided around the MOP501. However, the carrier CA2 of the differential unit 50, to which theMOP 501 is connected, does not rotate in the negative direction in anymode, and the above-described reverse rotation prevention device is notrequired, so it is possible to simplify (compactify) the configurationaround the MOP 501.

Next, control for switching from series-parallel mode to series modewill be described. FIG. 10 is a time chart that shows changes in thestates of the hybrid vehicle 1 at the time of switching fromseries-parallel mode to series mode. As shown in FIG. 10, control forswitching from series-parallel mode to series mode, which is executed bythe controller 100, will be described.

Control for switching from series-parallel mode to series mode isimplemented by causing the transmission unit 40 to switch from the powertransmission state to the neutral state (that is, by causing the clutchC1 or the brake B1 to switch from the engaged state to the releasedstate) and causing the clutch CS to switch from the released state tothe engaged state. FIG. 10 illustrates the case where, before time t1,the series-parallel mode is set in a low gear position Lo by engagingthe clutch C1.

When it is determined at time t1 to switch into series mode, thecontroller 100 reduces the reaction torque (negative torque) of thefirst MG 20 to zero after time t2, and begins to reduce C1 pressure inorder to start releasing the clutch C1. Thus, at time t3, the rotationspeed of the engine 10 and the rotation speed of the first MG 20 beginto decrease.

At time t4, the controller 100 starts synchronization control forsynchronizing the rotation speed of the first MG 20 with the rotationspeed of the engine 10. Specifically, the controller 100 increases therotation speed of the first MG 20 to a synchronization rotation speed atthe time of engagement of the clutch CS by changing the first MG torqueTm1 from zero to positive torque.

At time t5, the controller 100 begins to increase the CS pressure inorder to start engagement of the clutch CS. After that, at time t7, whenthe CS pressure reaches a predetermined engagement pressure andengagement of the clutch CS completes, the controller 100 causes thefirst MG 20 to generate electric power by setting the first MG torqueTm1 to negative torque again, thus starting the series mode.

An engine transmission torque Tec transmitted to the ring gear R2 inseries-parallel mode is not, transmitted to the ring gear R2 afterswitching into series mode (see FIG. 8 and FIG. 9). In consideration ofthis point, the controller 100 increases a second MG torque Tm2 aftertime t3. Thus, a decrease in driving force is suppressed by switchingfrom series-parallel mode to series mode.

In the example shown in FIG. 10, in consideration of the fact that therotation speed of the MOP 501 temporarily decreases as a result ofswitching from series-parallel mode to series mode, the controller 100operates the EOP 502 to increase the rotation speed of the EOP 502 fromtime t3 to time t6.

FIG. 11 is a nomograph that shows an example of changes in the statusesof the rotating elements when the drive mode is switched fromseries-parallel mode to series mode in a state where the rotation speedof the first MG 20 is higher than the rotation speed of the engine 10.In FIG. 11, the alternate long and short dashes line represents a commonline in the case where the brake B1 has been engaged just beforeswitching into series mode (just before the clutch CS is engaged). Thesolid line represents a common line just after switching into seriesmode (just after the clutch CS is engaged).

As shown in FIG. 11, when the rotation speed of the first MG 20 ishigher than the rotation speed of the engine 10 just before switchinginto series mode, the rotation speed of the first MG 20 decreases towardthe rotation speed of the engine 10 as a result of engagement of theclutch CS. At this time, because the rotation speed of the ring gear R2of the differential unit 50 almost does not change because of theinertia force of the hybrid vehicle 1, the rotation speed of the carrierCA2 of the differential unit 50 decreases with a decrease in therotation speed of the first MG 20 as shown in FIG. 11, so hydraulicpressure that is generated by the MOP 501 also decreases.

In consideration of such a phenomenon, when the rotation speed of thefirst MG 20 is higher than the rotation speed of the engine 10, thecontroller 100 predicts a decrease in hydraulic pressure due to atemporal decrease in rotation of the MOP 501 resulting from switchingfrom series-parallel mode to series mode, and increases the rotationspeed of the EOP 502 in advance. Thus, the amount of decrease inhydraulic pressure of the MOP 501 is compensated by the amount ofincrease in hydraulic pressure of the EOP 502.

On the other hand, when the drive mode is switched from series-parallelmode to series mode in a state where the rotation speed of the engine 10is higher than the rotation speed of the first MG 20, the rotation speedof the MOP 501 temporarily increases, so the controller 100 decreasesthe rotation speed of the EOP 502.

FIG. 12 is a nomograph that shows an example of changes in the statusesof the rotating elements when the drive mode is switched fromseries-parallel mode to series mode in a state where the rotation speedof the engine 10 is higher than the rotation speed of the first MG 20.In FIG. 12, the alternate long and short dashes line represents a commonline in the case where the brake B1 has been engaged just beforeswitching into series mode (just before the clutch CS is engaged). Thesolid line represents a common line just after switching into seriesmode (just after the clutch CS is engaged).

As shown in FIG. 12, when the rotation speed of the engine 10 is higherthan the rotation speed of the first MG 20 just before switching intoseries mode, the rotation speed of the first MG 20 increases toward therotation speed of the engine 10 as a result of engagement of the clutchCS. At this time, as shown in FIG. 12, the rotation speed of the carrierCA2 of the differential unit 50 increases with an increase in therotation speed of the first MG 20, so hydraulic pressure that isgenerated by the MOP 501 also increases.

In consideration of such a phenomenon, when the rotation speed of theengine 10 is higher than the rotation speed of the first MG 20, thecontroller 100 predicts an increase in hydraulic pressure due to atemporal increase in rotation of the MOP 501 resulting from switchingfrom series-parallel mode to series mode, and decreases the rotationspeed of the EOP 502 in advance. Thus, the amount of increase inhydraulic pressure of the MOP 501 is cancelled by the amount of decreasein hydraulic pressure of the EOP 502.

As described above, at the time of switching from series-parallel modeto series mode, the controller 100 changes the rotation speed of the EOP502 based on whether the rotation speed of the engine 10 is lower thanthe rotation speed of the first MG 20. Therefore, an increase ordecrease in hydraulic pressure due to a temporal change in rotation ofthe MOP 501 at the time of switching from series-parallel mode to seriesmode is compensated by hydraulic pressure of the EOP 502. Therefore, itis possible to supply necessary and sufficient hydraulic pressure evenin a period of transition of switching from series-parallel mode toseries mode.

Next, an alternative embodiment to the present embodiment will bedescribed. In the above-described embodiment, the case where the MOP 501is connected to the carrier CA2 of the differential unit 50 isillustrated. Instead, the MOP 501 may be connected to the sun gear S2 orring gear R2 of the differential unit 50. That is, the sun gear S2 orring gear R2 of the differential unit 50, as well as the carrier CA2, isrotatable even in a state where the carrier CA1 of the transmission unit40 is stopped as a result of a stop of the engine 10. Therefore, whenthe MOP 501 is connected to the sun gear S2 or ring gear R2 of thedifferential unit 50 as well, it is possible to operate the MOP 501 in astate where the engine 10 is stopped.

FIG. 13 is a view that shows a nomograph in series-parallel mode in thecase where the MOP 501 is connected to the ring gear R2 of thedifferential unit 50. When the MOP 501 is connected to the ring gear R2of the differential unit 50, and when the hybrid vehicle 1 is travelingforward as shown in FIG. 13, the ring gear R2 of the differential unit50 rotates in the positive direction irrespective of the operating stateof the engine 10. Therefore, it is possible to operate the MOP 501 evenin a state where the engine 10 is stopped.

When the MOP 501 is connected to the ring gear R2 of the differentialunit 50, the ring gear R2 rotates in the negative direction at the timewhen the vehicle moves backward, so the above-described reverse rotationprevention device just needs to be provided around the MOP 501. When theMOP 501 is connected to the sun gear S2 of the differential unit 50 aswell, the sun gear S2 can rotate in the negative direction, so theabove-described reverse rotation prevention device just needs to beprovided around the MOP 501.

The sun gear S2 and ring gear R2 of the differential unit 50 are rotatedwhen the vehicle is moving forward or backward in two-motor EV mode (seeFIG. 7). Therefore, when the MOP 501 is connected to the sun gear S2 orring gear R2 of the differential unit 50, it is possible to operate theMOP 501 even in two-motor EV mode.

The embodiment described above is illustrative and not restrictive inall respects. The scope of the invention is defined by the appendedclaims rather than the above description. The scope of the invention isintended to encompass all modifications within the scope of the appendedclaims and equivalents thereof.

What is claimed is:
 1. A hybrid vehicle comprising: an internalcombustion engine; a first rotary electric machine; a second rotaryelectric machine configured to output power to a drive wheel; a powertransmission unit including an input element, an output element and anengaging portion, the input element being configured to receive powerfrom the internal combustion engine, the output element being configuredto output power input to the input element, and the engaging portionbeing configured to switch between a non-neutral state where power istransmitted between the input element and the output element and aneutral state where power is not transmitted between the input elementand the output element; a differential unit including a first rotatingelement, a second rotating element and a third rotating element, thefirst rotating element being connected to the first rotary electricmachine, the second rotating element being connected to the secondrotary electric machine and the drive wheel, the third rotating elementbeing connected to the output element, and the differential unit beingconfigured such that, when rotation speeds of any two of the firstrotating element, the second rotating element and the third rotatingelement are determined, a rotation speed of the remaining one of thefirst rotating element, the second rotating element and the thirdrotating element is determined; a clutch configured to switch between anengaged state where power is transmitted from the internal combustionengine to the first rotary electric machine and a released state wheretransmission of power from the internal combustion engine to the firstrotary electric machine is interrupted, power from the internalcombustion engine being transmitted to the first rotary electric machinethrough at least one of a first path or a second path, the first pathbeing a path through which power is transmitted from the internalcombustion engine to the first rotary electric machine via the powertransmission unit and the differential unit, the second path being apath through which power is transmitted from the internal combustionengine to the first rotary electric machine, being different from thefirst path, not including the differential unit, and the clutch beingprovided in the second path; and a mechanical oil pump configured togenerate hydraulic pressure for activating the power transmission unitand the clutch, the mechanical oil pump being configured to be driven bypower that is transmitted from any one of the first rotating element,second rotating element and third rotating element of the differentialunit.
 2. The hybrid vehicle according to claim 1, wherein thedifferential unit is a planetary gear including a sun gear, a ring gear,pinions that are in mesh with the sun gear and the ring gear, and acarrier that supports the pinions such that the pinions are rotatable,the first rotating element, the second rotating element and the thirdrotating element are respectively the sun gear, ring gear and carrier ofthe planetary gear, the mechanical oil pump is connected to the carrier,and the mechanical oil pump is configured to be driven by power that istransmitted from the carrier.
 3. The hybrid vehicle according to claim2, further comprising: an electric oil pump configured to generatehydraulic pressure for activating the power transmission unit and theclutch; and a controller configured to control the electric oil pump,the controller being configured to, at the time of switching fromseries-parallel mode to series mode, change a rotation speed of theelectric oil pump based on whether a rotation speed of the internalcombustion engine is lower than a rotation speed of the first rotaryelectric machine, wherein the series-parallel mode is a mode in whichthe hybrid vehicle travels in a state where the power transmission unitis placed in the non-neutral state and the clutch is placed in thereleased state, and the series mode is a mode in which the hybridvehicle travels in a state where the power transmission unit is placedin the neutral state and the clutch is placed in the engaged state. 4.The hybrid vehicle according to claim 3, wherein the controller isconfigured to, at the time of switching from the series-parallel mode tothe series mode, increase the rotation speed of the electric oil pumpwhen the rotation speed of the internal combustion engine is lower thanthe rotation speed of the first rotary electric machine, and decreasethe rotation speed of the electric oil pump when the rotation speed ofthe internal combustion engine is higher than the rotation speed of thefirst rotary electric machine.